Synchronizing system



April 5, 1938. M. K. TAYLOR ET AL I 7 SYNCHRONIZING SYSTEM Fi led April 18. 1935 Patented Apr. 5, 1938 UNITED STATE SYNGHRONIZIN G SYSTEM Maurice Kenyon- Taylor and :Sidney- Atkinson, Hollinwood, England, assignors to Ferranti Electric Inc., New York, N ..Y..

Application April 18, 1935, SeriaILNo: 1?;088 In. Great Britain April24; 1934= chanically scanned television receivers is required to be maintained at'a substantially constant angular velocity with respect to the frequency'of' an external electrical timing wave.

In most systems for attaining the above object, a' synchronizing motor is employed, the use 1'6 of which may, however; lead to the setting up of angular oscillations superimposed on the synchronous speed by reason ofthe synchronizing couple and the inertia of the body which is being syn-- chronized; under these conditions the rotating 1E body is'said to be hunting;

The main object of the present'invention is to provide means in connection with the reception of television signals, whereby optical means for locating the position of the final image are controlled irrespective of any hunting of the rotor of the scanning device.

Referring to the accompanying diagrammatic drawing:-

Figure 1 illustrates part of a television receiver embodying the present invention, and

Figure 2 is a circuit diagram illustrating a convenient arrangement of mixing circuit.

In carrying the invention into efiect according to one convenient form as illustrated in Figure 1, we provide an amplifier device 3 having a pair of input terminals 25, 25 and two pairs 26, 26 and 21, 21 of output terminals, the input terminals 25, 25 being connected respectively to an aerial l and an earth lead 2 whilst one pair 26, 26 of output terminals is connected to a light modulation circuit (not shown), as is customary; fina1 ly, the other pair 21, 21 of output terminals is connected to the ends of an electromagnet coil 4. This electromagnet coil is mounted on a core 5 having pole-pieces 28, 28 associated with a rotor 6 having a notched periphery forming teeth.

The magnet is conveniently of the form described in British specification No. 31,964 of 1933. Also co-operating with the toothed disc 6 is a wave generator comprising a permanent magnet 8 having two pole pieces I, 1, each carrying a coil I l, l I, the permanent magnet being mounted on an arcuate bracket l3 sliding on pins I4, I 4 and capable of being moved by a pinion l5 engaging a curved rack embodied in the bracket.

The output from the coils H, II is led to one pair of input terminals 9, 9, of a mixing circuit "5, and from another pair of input terminals II], II! leads II are taken to the ends of the elec-- tromagnet coil first mentioned above.

The mixing circuit conveniently comprises a pentode' valve 33 the twocontrol grids 34, 35of which are associated respectively with resistances 36, 31; I

The resistance 36 is connectedtoterminals- ID by way of'a condenser 38 and the resistance 31 is connected to terminals 9by way of a condenser 39; the connection to the grids' b'eing variable to enable the voltages applied to the grids to be equalized.

The cathode is connected to 'one'of the terminals 29 and the anode is connected by way of a battery 40 to the other terminal 295 l 'I'heoutput terminalsZQ} 29 of this circuit are connected, if desiredby way of an amplifier, to a coil l8 mounted-in the air gaps between three magnet pole pieces I9, 20, 2| of which l9 and 2| are caused to assume opposite fixed polarity. The coil I 8 is carried on a shaft 22. two hair springs 23 and 24 being provided to urge the coil into a predetermined plane. The terminals 29 convey current to and from the coil l8 by way of the hair springs. Mounted also upon the shaft 22 is a mirror 30 so disposed as to reflect modulated light on to a screen 32 after being refiected by a mirror screw device 23 and after passing through an object lens 3|.

The mirror-screw 23 is rigidly carried on the spindle 24 which also supports rigidly the disc 6.

In operation, the incomingsynchronizing signals in the aerial-earth circuit l, 2 ultimately cause the electromagnet 4 to tend to maintain the notched disc 6 in step with them. By virtue of the movement of the notched disc across the magnetic path of the wave generator, an alternating E. M. F. is generated whose frequency is directly proportional at all times to the instantaneous speed of rotation of the disc. This alternating E. M. F. is mixed in the circuit IS with part of the amplified incoming synchronizing signal and on rectification produces a direct E. M. F. whose amplitude varies with the phase difference between the synchronizing wave from the amplifier 3 and the E. M. F. produced by the wave generator 1.

The direct E. M. F. so produced, with or without amplification, is applied to the coil l8 and thus the position of the light on the screen 32 is varied in accordance with the phase displacement between the incoming synchronizing wave and that generated in the coils l I, ll of the wave generator.

Adjustment of the phase angle may be, performed by adjustment of the position of the arcuate bracket.

If desired the toothed wheel 6 may be mounted on a spindle geared to a further spindle carrying a mirror screw or drum.

According to a modification, the toothed disc 6 is spring mounted and the poles 28 are rigid with the core 5, the wave generator pole pieces cooperating with a further toothed disc mounted rigidly on a shaft carrying the mirror screw 23*.

With this modification resilience of the mounting of the pole shoes 28 is thus transferred to that of the disc 6, a separate disc rigid with the shaft carrying the mirror screw 23 co-operating with the pole pieces 1, l.

In a further modification the rotating scanning body being synchronized may be geared to the toothed disc instead of being rigid therewith.

The means for varying the angle of the wave generator may be modified in any convenient manner.

In a further modification of the mixing portion It of the system, the leads I! from the amplifier 3 to the input terminals I0, ID of the mixer circuit l5 and/or the leads from the wave generator to the input terminals 9, 9 of the mixer circuit are fed by way of suitable couplings, e. g., transformers, resistance-capacity couplings, etc., to a series circuit comprising the two inputs, a rectifier and a resistance load which may be shunted by a condenser.

Having now described our invention, what we claim as new and desire to secure by Letters Patent is:--

1. A method of image framing in television which consists in controlling the direction of part of the path of a modulated light beam by applying synchronizing impulses to a mixing cirsuit and to a synchronous motor, causing said synchronous motor to drive a scanning device and a wave generator the voltage wave generated by said voltage generator corresponds with the instantaneous angular velocity of the scanning device, applying said voltage wave to said mixing circuit to produce a resultant varying electrical output and applying said resultant electrical output to modulated light beam defleeting device other than that used for scanning.

2. A synchronizing system having means for controlling the direction of part of the path of a modulated light beam including a synchronous motor, a mechanical scanning device, a driving connection between said synchronous motor and said mechanical scanning device, a wave generator in rigid association with said scanning device, a mixing circuit, means for applying the output from said wave generator to said mixing circuit, means for applying incoming synchronizing impulses to said synchronous motor and to said mixing circuit, additional meansfor deflecting said modulated light beam, means for deflecting said additional means, and means for applying the resultant output from said mixing circuit to said deflecting means to deflect said additional means in accordance with the amplitude of the said resultant output whereby the position of the final image is located irrespective 

